1. Field of the Invention
The present invention relates to a head suspension assembly for a data storage system, and, more particularly, to such an assembly wherein the head suspension is manufactured using a laminate or clad composite sheet metal having one or more etch-stop layers formed therein.
2. Description of the Prior Art
Direct access storage devices of the type known as "Winchester" disk drives, or merely "disk drives", are well known in the computer industry. Disk drives store information on concentric, recorded tracks written on one or more rotatable magnetic recording disks. A magnetic head or transducer element is provided for each such disk, and moves from track to track, to either read previously stored information or to record information on the magnetic tracks ("read"-"write", respectively). The electromagnetic transducer typically is carried in a slider body mechanism that is supported over the surface of a rotating disk by a self-acting, hydrodynamic air bearing.
The slider body/transducer combination is referred to collectively as a "head", and it is attached to a suspension assembly that suspends and loads the head toward the disk surface. The suspension assembly is in turn connected to a rotary or linear actuator that controllably moves the head from track to track on the disk, in response to electrical signals generated by controlling circuitry. To aid in accurate tracking, the head is attached to the suspension assembly in a manner that permits the head to gimbal. In this manner, variations in head orientation necessitated by the radial repositioning of the head, relative to the magnetic disk surface, can be easily accommodated.
The trend towards increasing density of memory storage devices has not escaped disk drives, which have decreased in size while their data storage capacity has increased. Continuing improvements in the magnetic recording media, the head designs, and the control circuitry have permitted the data tracks to become smaller and closer together. The large suspensions used in older disk drives are too stiff to support the required high precision positional adjustment of the smaller, lighter-weight heads and sliders. Lighter and more selectively flexible suspension systems are required. Such suspensions must be increasingly flexible in the vertical direction to accurately track with the lighter heads, while remaining rigid in the horizontal or lateral direction to prevent unwanted side-to-side movement and the resultant mistracking.
During the initial period of disk size reductions, this problem was addressed by utilizing suspension members of ever decreasing thickness, with proportionally increasing ratios of width to thickness. However, as improvements in head and control circuit technology continued to permit further downsizing, stainless steel, the material of choice for manufacturing suspension members, reached its lower milling thickness. Below about 0.025 mm. in thickness, irregularities in stainless steel grain structure result in thickness variations that make steel of such dimensions unsuitable for use in suspensions.
With mechanical methods for shaping the extremely thin metal stock ruled out, the manufacturers of suspension assemblies have turned to photo-chemical etching techniques. This well-known technology for creating printed circuit boards of unfathomable complexity appeared to offer great promise for use in creating the small geometries required to achieve the desired bending characteristics in suspension assemblies. After the initial milling and stamping operations, a photo-etch resist pattern is applied to a suspension member blank. A chemical solvent is applied to remove metal from the exposed areas, thereby achieving the fine geometries necessary to the operation of the suspension member. The removal of metal from selected locations of the suspension member, and the resultant variations in suspension metal thickness, both reduce the weight of the suspension member and change its dynamic characteristics.
The unremitting advance towards ever lighter and more flexible suspension assemblies has resulted in suspensions of increasingly elaborate geometries. The tolerances required to achieve such geometries are rapidly approaching the process limits for photo-resist etching. While the depth of material removal is substantially a linear function related to the amount of time the metal surface is exposed to the chemical solvent, there are a number of variables that affect the ability to precisely control the amount of metal removed. Where, as here, extremely small tolerances are required, it becomes difficult to consistently achieve the required etch depth due to unavoidable variations in both temperature, etching time, and chemical contamination. In addition to variances in the concentration of the solvent, as well as the flow velocity of the solvent (or agitation), impurities in both the solvent and the metal being etched, and variances in the metal thickness, can all create process control problems that affect the end result of the fabrication process. As a result, there are practical limitations to the degree of control exercisable over the depth and shape of certain fine or small geometries formed in the suspension metal blank.
Accordingly, there is a need, in producing light, flexible, small suspension assemblies, for a process control technique that, when used with photo-resist etching, will permit a greater degree of control with respect to the etch depths achieved in the metal suspension assemblies.